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June 2013 Summary Report: UCPRC-SR-2013-03
Authors: D. Jones, F. Farshidi, and J.T. Harvey
Partnered Pavement Research Center (PPRC) Contract Strategic Plan Element 4.41.2: Environmental Impacts and Energy Efficiency of Warm Mix Asphalt
PREPARED FOR: California Department of Transportation Division of Research, Innovation, and System Information Office of Materials and Infrastructure
PREPARED BY:
University of California Pavement Research Center
UC Davis, UC Berkeley
DOCUMENT RETRIEVAL PAGE Summary Report: UCPRC-SR-2013-03
Title: Warm-Mix Asphalt Study: Summary Report on Rubberized Warm-Mix Asphalt Research
Authors: David Jones, Frank Farshidi, and John T. Harvey
Caltrans Technical Lead: T. Joe Holland (Caltrans) and Nathan Gauff (CalRecycle)
Prepared for: Caltrans and CalRecycle
FHWA No.: CA142385C
Work submitted: 03/05/2014
Date June 2013
Strategic Plan Element No: 4.41.2
Status: Final
Version No.: 1
Abstract: Warm-mix asphalt (WMA) is a relatively new technology. It was developed in response to needs for reduced energy consumption and stack emissions during the production of asphalt concrete, long hauls, lower placement temperatures, improved workability, and better working conditions for plant and paving crews. Studies in the United States and Europe indicate that significant reductions in production and placement temperatures, and, potentially, in related emissions are possible. However, concerns exist about how these lower production and placement temperatures could influence asphalt binder aging and, consequently, short- and long-term performance, specifically rutting. The overall objective of the warm-mix asphalt study was to determine whether the use of technologies that reduce the production and construction temperatures of asphalt concrete mixes influences performance of the mix. The objective of this part of the study was to identify limitations and benefits of using warm-mix asphalt technologies in rubberized asphalt mixes. The testing completed in this phase of the warm-mix asphalt study provided no results to suggest that warm-mix technologies should not be used in rubberized mixes in California, provided that standard specified mix design, construction, and performance limits for hot-mix asphalt are met. The use of warm-mix asphalt technologies in rubberized asphalt mixes has clear benefits when compared to hot mixes. These include significant reductions in, or even elimination of, smoke and odors, lower emissions, improved workability, better working conditions, and better performance on projects with long hauls or where mixes are placed under cool conditions. The slightly higher costs of using warm-mix technologies are outweighed by these benefits. Based on the findings of this study, the use of warm-mix asphalt technologies in rubberized asphalt mixes is encouraged, especially on projects in urban areas and on those with long hauls and/or where mixes are placed under cool conditions. Given that warm-mix asphalt may be produced at significantly lower temperatures than hot-mix asphalt (with associated lower aggregate heating temperatures), moisture sensitivity, especially on water-based warm-mix asphalt technologies, should be closely monitored in mix-design and quality control/quality assurance testing.
Keywords: Warm-mix asphalt, rubberized hot-mix asphalt, rubberized warm-mix asphalt, asphalt emissions
Proposals for implementation: Continue with statewide implementation.
Related documents: Research Reports, RR-2011-02, RR-2011-03, RR-2013-02, RR-2013-03.
Signatures:
D. Jones 1st Author
J.T. Harvey Technical Review
D. Spinner Editor
J.T. Harvey Principal Investigator
T.J. Holland Caltrans Technical Lead
T.J. Holland Caltrans Contract Manager
UCPRC-SR-2013-03 i
DISCLAIMER STATEMENT
This document is disseminated in the interest of information exchange. The contents of this report reflect
the views of the authors who are responsible for the facts and accuracy of the data presented herein. The
contents do not necessarily reflect the official views or policies of the State of California or the Federal
Highway Administration. This publication does not constitute a standard, specification or regulation.
Product names are used in this report for clarification purposes only. The University of California, State
of California, and the Federal Highway Administration do not endorse the use of any specific warm-mix
technology.
For individuals with sensory disabilities, this document is available in Braille, large print, audiocassette,
or compact disk. To obtain a copy of this document in one of these alternate formats, please contact: the
California Department of Transportation, Division of Research, Innovation, and System Information,
MS-83, P.O. Box 942873, Sacramento, CA 94273-0001.
PROJECT OBJECTIVES
The objective of the Caltrans/UCPRC warm-mix asphalt study is to determine whether the use of
technologies that reduce the production and construction temperatures of asphalt concrete mixes
influences performance of the mix. The objective of this part of the study was to identify limitations and
benefits of using warm-mix asphalt technologies in rubberized asphalt mixes.
ACKNOWLEDGEMENTS
The University of California Pavement Research Center acknowledges the assistance and interest of Ms.
Nahid Hosseinzadeh (retired), Mr. Joseph Peterson and Dr. Joe Holland from Caltrans; Mr. Nate Gauff
and Mr. Robert Fujii from CalRecycle; and Dr. Peter Green and Dr. Isabel Faria, University of California,
Davis.
ii UCPRC-SR-2013-03
STUDY REPORTS
The documents prepared during the rubberized warm-mix asphalt study document data from test track
construction, Heavy Vehicle Simulator (HVS) tests, laboratory performance tests, investigations into
emissions and binder aging, and longer-term field studies. This suite of documents includes the following
series of first-level analysis reports, a technical memorandum, and this summary report a series of first-
level analysis reports and this summary report.
1. Warm-Mix Asphalt Study: Test Track Construction and First-Level Analysis of Phase 3a HVS
and Laboratory Testing (Rubberized Asphalt, Mix Design #1). (UCPRC-RR-2011-02)
2. Warm-Mix Asphalt Study: Test Track Construction and First-Level Analysis of Phase 3b HVS
and Laboratory Testing (Rubberized Asphalt, Mix Design #2). (UCPRC-RR-2011-03)
3. Warm-Mix Asphalt Study: Evaluation of Rubberized Hot- and Warm-Mix Asphalt with Respect to
Binder Aging. (UCPRC-RR-2013-02)
4. Warm-Mix Asphalt Study: Evaluation of Rubberized Hot- and Warm-Mix Asphalt with Respect to
Emissions. (UCPRC-RR-2013-03)
5. Warm-Mix Asphalt Study: Field Test Performance Evaluation. (UCPRC-TM-2013-08)
6. Warm-Mix Asphalt Study: Summary Report on Rubberized Warm-Mix Asphalt Research.
(UCPRC-SR-2013-03)
UCPRC-SR-2013-03 iii
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iv UCPRC-SR-2013-03
TABLE OF CONTENTS STUDY REPORTS .....................................................................................................................................iii 1. INTRODUCTION ............................................................................................................................. 1
1.1 Background ............................................................................................................................... 1 1.2 Project Objectives ...................................................................................................................... 1 1.3 Structure and Content of this Report ......................................................................................... 2 1.4 Terminology .............................................................................................................................. 2
2. HEAVY VEHICLE SIMULATOR TESTING: RWMA-G .......................................................... 3 2.1 Introduction ............................................................................................................................... 3 2.2 Methodology ............................................................................................................................. 3 2.3 Test Track Construction ............................................................................................................ 3 2.4 Heavy Vehicle Simulator (HVS) Testing .................................................................................. 4 2.5 Key Findings ............................................................................................................................. 4 2.6 Recommendations ..................................................................................................................... 6 2.7 Reports....................................................................................................................................... 6
3. LABORATORY TESTING: RWMA-G PERFORMANCE ........................................................ 7 3.1 Introduction ............................................................................................................................... 7 3.2 Methodology ............................................................................................................................. 7 3.3 Findings ..................................................................................................................................... 7 3.4 Reports....................................................................................................................................... 8
4. LABORATORY TESTING: BINDER AGING ............................................................................. 9 4.1 Introduction ............................................................................................................................... 9 4.2 Methodology ............................................................................................................................. 9 4.3 Findings ..................................................................................................................................... 9 4.4 Recommendations ................................................................................................................... 10 4.5 Reports..................................................................................................................................... 10
5. LABORATORY TESTING: EMISSIONS .................................................................................. 11 5.1 Introduction ............................................................................................................................. 11 5.2 Methodology ........................................................................................................................... 11 5.3 Findings ................................................................................................................................... 11 5.4 Recommendations ................................................................................................................... 12 5.5 Reports..................................................................................................................................... 12
6. LONG-TERM FIELD PERFORMANCE..................................................................................... 13 6.1 Introduction ............................................................................................................................. 13 6.2 Methodology ........................................................................................................................... 13 6.3 Findings ................................................................................................................................... 13 6.4 Reports..................................................................................................................................... 14
7. CONCLUSIONS AND RECOMMENDATIONS ......................................................................... 15 7.1 Conclusions ............................................................................................................................. 15 7.2 Recommendations ................................................................................................................... 15
REFERENCES ........................................................................................................................................... 17
UCPRC-SR-2013-03 v
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vi UCPRC-SR-2013-03
1. INTRODUCTION
1.1 Background
Warm-mix asphalt (WMA) is a relatively new technology. It was
developed in response to demands for reduced energy
consumption and stack emissions during the production of
asphalt concrete, for better performance after long hauls, lower
placement temperatures, improved workability, and better
working conditions for plant and paving crews. Studies
performed in the United States and in Europe indicate that
significant reductions in production and placement temperatures
and of potentially related emissions are possible. However,
concerns exist about how these lower production and placement
temperatures might influence asphalt binder aging and,
consequently, both short- and long-term performance,
specifically rutting.
The California Department of Transportation (Caltrans)
expressed interest in warm-mix asphalt with a view to reducing stack emissions at plants, to allow longer
haul distances between asphalt plants and construction projects, to improve construction quality
(especially during nighttime closures), to improve working conditions during construction, and to extend
the annual period for paving. However, the use of warm-mix asphalt technologies requires incorporating
an additive into the mix, and/or changes in production and construction procedures, specifically related to
temperature, which could influence both the short- and long-term performance of the pavement, as well as
emissions during production and placement. Consequently, the need for research was identified by
Caltrans to address a range of concerns related to these changes before statewide implementation of the
technology is approved.
1.2 Project Objectives
The research presented in this report is part of Partnered Pavement Research Center Strategic Plan
Element 4.41.2 (PPRC SPE 4.41.2), titled “Environmental Impacts and Energy Efficiency of Warm Mix
Asphalt,” which was undertaken for Caltrans and the California Department of Resources, Recycling, and
Recovery (CalRecycle) by the University of California Pavement Research Center (UCPRC). This study
follows an earlier three-phase project (SPE 4.18) that assessed the performance of warm-mix asphalt in
Hot-mix asphalt
Warm-mix asphalt
UCPRC-SR-2013-03 1
laboratory, accelerated loading, and full-scale field trials on California highways (1-5). The overall
objective of the warm-mix asphalt study was to determine whether the use of technologies that reduce the
production and construction temperatures of asphalt concrete mixes influences performance of the mix.
The objective of this part of the study was to identify limitations and benefits of using warm-mix asphalt
technologies in rubberized asphalt mixes.
1.3 Structure and Content of this Report
This report presents a summary of all the work carried out to date on rubberized warm-mix asphalt as part
of the larger study on warm-mix asphalt undertaken to meet the project objective. Each chapter
summarizes a task, as follows:
• Chapter 2: Heavy Vehicle Simulator testing of gap-graded rubberized warm-mix asphalt (RWMA-G)
• Chapter 3: Laboratory testing of gap-graded rubberized warm-mix asphalt (RWMA-G) • Chapter 4: Laboratory testing to assess the effect of warm-mix asphalt technologies on asphalt
binder aging • Chapter 5: Laboratory testing to assess the effect of warm-mix asphalt technologies on emissions
during placement • Chapter 6: Long-term field performance • Chapter 7: Conclusions and preliminary recommendations
1.4 Terminology
The term “asphalt concrete” is used in this report as a general descriptor for asphalt concrete surfacings.
The terms “hot-mix asphalt (HMA)” and “warm-mix asphalt (WMA)” are used as descriptors to
differentiate between the control and warm-mixes discussed in this study.
2 UCPRC-SR-2013-03
2. HEAVY VEHICLE SIMULATOR TESTING: RWMA-G
2.1 Introduction
This phase of the study, which investigated gap-graded
rubberized asphalt concrete, was based on a workplan approved
by Caltrans and included the design and construction of a test
track and accelerated load testing using a Heavy Vehicle
Simulator (HVS) to assess rutting behavior. A series of
laboratory tests on specimens sampled from the test track to
assess rutting and fatigue cracking performance and moisture sensitivity were also undertaken; those
results are discussed in Chapter 3.
2.2 Methodology
The study compared the performance of two gap-graded rubberized asphalt control mixes, which were
produced and constructed at conventional hot-mix asphalt temperatures (320°F [160°C]), with seven
warm-mixes, produced and compacted at between 36°F (20°C) and 60°F (35°C) lower than the control.
The mixes were produced at two different asphalt plants and are reported as Phase 3a and Phase 3b
(Phases 1 and 2 investigated dense-graded mixes with a conventional binder [1-3]). Phase 3a included
mixes produced at Granite Construction’s Bradshaw Plant using Cecabase RT®, Evotherm DATTM, and
Gencor Ultrafoam GXTM warm-mix technologies. Phase 3b included mixes produced at the George Reed
Marysville Plant using Astec Double Barrel Green®, Advera WMA®, RedisetTM, and Sasobit® technologies.
2.3 Test Track Construction
The test track was constructed at the University of California Pavement Research Center (UCPRC) in
Davis, California, in April 2010. Design and construction was a cooperative effort between Caltrans, the
UCPRC, Granite Construction, George Reed Construction, Teichert Construction, and the seven warm-
mix technology suppliers. The test track was 360 ft. by 50 ft. (110 m by 15 m) divided into nine test
sections (two controls and seven warm-mixes). The pavement structure consisted of the ripped and
recompacted subgrade, 1.3 ft. (400 mm) of imported aggregate base, one 0.2 ft. (60 mm) lift of dense-
graded hot-mix asphalt, and one 0.2 ft. (60 mm) lift of gap-graded rubberized hot-mix (RHMA-G) or
warm-mix (RWMA-G) asphalt concrete. Each asphalt plant prepared a mix design. No adjustments were
made to these mix designs to accommodate the warm-mix technologies. Target production temperatures
Heavy Vehicle Simulator
UCPRC-SR-2013-03 3
were not set; instead the warm-mix technology suppliers set their own temperatures based on experience,
ambient temperatures, and haul distance.
The production temperature for the Granite Bradshaw RHMA-G control mix was 320°F (160°C) and
266°F (130°C), 248°F (125°C), and 284°F (140°C) for the Cecabase, Evotherm, and Gencor warm-mixes,
respectively. Temperatures for the George Reed Marysville RHMA-G control mix was 335°F (166°C) and
295°F (145°C), 295°F (145°C), 285°F (140°C), and 300°F (149°C) for the Advera, Astec, Rediset and
Sasobit warm-mixes, respectively.
2.4 Heavy Vehicle Simulator (HVS) Testing
Heavy Vehicle Simulator (HVS) testing commenced in June 2010 after a six-week curing period and was
completed in January 2011. Additional testing on three of the sections was conducted in August and
September 2011. This testing compared early rutting performance at elevated temperatures (pavement
temperature of 122°F at 2.0 in. [50°C at 50 mm]), starting with a 9,000 lb. (40 kN) load on a standard
dual-wheel configuration and a unidirectional trafficking mode.
2.5 Key Findings
Key findings from the study include the following:
• A consistent subgrade was prepared and consistent base-course and underlying dense-graded hot-mix asphalt concrete layers were constructed on the test track using materials sourced from a nearby quarry and asphalt plant. Thickness and compaction of the base and bottom layer of asphalt were consistent across the test track.
• Minimal asphalt plant modifications were required to accommodate the warm-mix technologies, and the delivery systems were approved under the Caltrans Material Plant Quality Program.
• No problems were noted with producing the asphalt mixes at the lower temperatures. Target mix production temperatures set by the warm-mix technology providers were all achieved. There was very little variation in mix properties among the four mixes produced in the Phase 3a study, but there was some variation in binder content among the six mixes produced in Phase 3b due to plant control problems, with the Rediset mix having a significantly higher binder content compared to the design and to the other mixes. Hveem stabilities, determined after three different aging regimes, exceeded the minimum requirement by a considerable margin. Curing did not appear to influence the stability. No moisture was measured in the mixes after production.
• Compaction temperatures differed considerably among the mixes and were consistent with production temperatures. The mixes produced at lower temperatures lost heat at a slower rate during transport and placement than the mixes produced at the higher temperatures, as expected. The lower temperatures in the warm-mixes did not appear to influence the paving or compaction operations, and interviews with the paving crew after construction revealed that no problems were experienced at the lower temperatures. Improved working conditions were identified as an advantage.
4 UCPRC-SR-2013-03
• Smoke and odors were significantly more severe on the control sections compared to the warm-mix sections.
• Mix workability, determined through observation of and interviews with the paving crew, was considerably better on the warm-mix sections compared to the controls. General consistency of thickness across the track was considered satisfactory and representative of typical construction projects.
• Compaction across the test track appeared to be consistent, confirming that adequate compaction can be achieved on rubberized warm-mixes at lower temperatures. Based on observations from the test track construction and interviews with roller operators, optimal compaction temperatures and rolling patterns will differ between the different warm-mix technologies. In addition, roller operators will need to consider that there might be differences in roller response between warm-mix and conventional hot mixes, and that rolling operations and patterns may need to be adjusted to ensure that optimal compaction is always achieved.
• HVS trafficking indicated a difference in performance between the mixes from the two asphalt plants: + In Phase 3a, HVS trafficking on each of the four sections revealed that the duration of the
embedment phases on all sections were similar; however, the depth of the ruts at the end of the embedment phases differed slightly among the sections, with the Gencor (0.26 in. [6.5 mm]) and Cecabase (0.22 in. [5.5 mm]) having less embedment than the Control and Evotherm sections, which had similar embedment (0.31 in. [7.9 mm]). Rut rate (rutting per load repetition) after the embedment phase on the Control and Evotherm sections was almost identical. On the Gencor and Cecabase sections, rut rate was considerably slower than the Control after the embedment phase. The difference in performance between the three warm-mix sections is attributed in part to the lower production and paving temperatures of the Evotherm mix compared to the other warm mixes, as well as to the thickness of the asphalt layers (the Evotherm section had thinner asphalt layers than the Control and Cecabase sections). The duration of the tests to terminal rut (0.5 in. [12.5 mm]) on the five sections varied from 42,000 load repetitions on the Evotherm section to 200,000 load repetitions on the Cecabase section.
+ In Phase 3b, HVS trafficking on four of the five sections indicated generally consistent performance among the mixes. Unexpected poor performance was measured on the Advera section (Section 626HA) so additional tests on this section as well as on the Control and Sasobit sections were undertaken to determine the cause and to eliminate possible seasonal and machine-related testing variables. The cause of this poor performance was attributed to a combination of high subgrade moisture content and thinner combined asphalt layers, which were identified during a forensic investigation. The duration of the embedment phases on all sections except the Advera section were similar. Apart from the Advera section, the depth of the ruts at the end of the embedment phases differed only slightly between sections, with the Astec section (0.3 in. [7.5 mm]) having a slightly deeper embedment than the Control, Sasobit, and Rediset sections, which had similar embedment (0.26 in. [6.5 to 6.7 mm]). Rut rate after the embedment phase on the Control and Sasobit sections was almost identical. The rut rate was slightly higher on the Astec and Rediset sections, and was attributed to some moisture in the asphalt layer and subgrade in the Astec section (determined during the forensic investigation), and to the higher binder content on the Rediset section. Although lower production and paving temperatures typically result in less oxidation of the binder, which can influence early rutting performance,
UCPRC-SR-2013-03 5
differences in production and placement temperatures did not appear to influence performance in this set of tests. The duration of the tests to terminal rut on the five sections varied from 73,500 load repetitions on the Advera section to 365,000 load repetitions on the Sasobit section.
2.6 Recommendations
HVS test results in this and earlier phases showed differences in early rutting performance between
conventional and rubber mixes, between mixes tested after different curing periods, and between
pavements subjected to mostly shade and mostly sun, respectively. Consequently, the study recommended
that consideration be given to further investigation into the effects of warm-mix asphalt technologies and
production and placement of warm-mixes at lower temperatures on binder oxidation/aging rates and
related performance over the life of the asphalt surfacing.
2.7 Reports
The following reports were prepared for this phase of the study:
1. JONES, D., Wu, R., Tsai, B. and Harvey, J. 2011. Warm-Mix Asphalt Study: Test Track
Construction and First-Level Analysis of Phase 3a HVS and Laboratory Testing (Rubberized
Asphalt, Mix Design #1). Davis and Berkeley, CA: University of California Pavement Research
Center. (UCPRC-RR-2011-02).
2. JONES, D., Wu, R., Tsai, B. and Harvey, J. 2011. Warm-Mix Asphalt Study: Test Track
Construction and First-Level Analysis of Phase 3b HVS and Laboratory Testing (Rubberized
Asphalt, Mix Design #2). Davis and Berkeley, CA: University of California Pavement Research
Center. (UCPRC-RR-2011-03).
6 UCPRC-SR-2013-03
3. LABORATORY TESTING: RWMA-G PERFORMANCE
3.1 Introduction
This phase of the study was carried out in conjunction with the
accelerated load testing discussed in Chapter 2 to compare
laboratory performance with performance under accelerated
loading, and to identify whether the warm-mix technologies
influenced other performance parameters, such as fatigue
cracking and moisture sensitivity.
3.2 Methodology
Specimens were sampled from each section on the test track discussed in Chapter 2 approximately six
weeks after construction. The laboratory test program included shear testing, wet and dry fatigue testing,
Hamburg Wheel-Track testing, and determination of the wet-to-dry tensile strength ratio.
3.3 Findings
The laboratory test results indicate that use of the warm-mix technologies assessed in this study, which
were produced and compacted at lower temperatures, did not significantly influence the performance of
the asphalt concrete when compared to control specimens produced and compacted at conventional hot-
mix asphalt temperatures. Laboratory test results were influenced by mix production temperatures, actual
binder content, specimen air-void content, actual stress and strain levels, and actual test temperature.
Variations in these parameters need to be taken into consideration when comparing performance between
the different mixes. Specific observations from the laboratory testing for the two different mix designs
include these:
• Phase 3a + Shear performance of the Evotherm and Cecabase mixes did appear to be negatively influenced
in part by the lower mix production and construction temperatures, which would have resulted in less oxidation of the binder and consequent lower stiffness of the mix. Rutting performance under accelerated load testing (HVS) did not appear to be affected, however. Fatigue performance and moisture sensitivity also did not appear to be affected during the HVS testing.
+ The Gencor (water injection technology) mix appeared to have lower moisture resistance compared to the other three mixes in all the moisture sensitivity tests, but it still met Caltrans-specified performance requirements in most instances. This mix was produced at a higher temperature than the other two warm-mixes and, like the other mixes, samples taken from the silo contained no moisture.
Hamburg Wheel Track Test
UCPRC-SR-2013-03 7
• Phase 3b + Laboratory performance in all tests appeared to be mostly dependent on air-void content and
binder content, as expected, and less dependent on mix production temperature. + The water-based warm-mix technology mixes (Advera and Astec) appeared to have lower
moisture resistance compared to the other three mixes in all the moisture sensitivity tests.
3.4 Reports
The following reports were prepared for this phase of the study:
1. JONES, D., Wu, R., Tsai, B. and Harvey, J. 2011. Warm-Mix Asphalt Study: Test Track
Construction and First-Level Analysis of Phase 3a HVS and Laboratory Testing (Rubberized
Asphalt, Mix Design #1). Davis and Berkeley, CA: University of California Pavement Research
Center. (UCPRC-RR-2011-02).
2. JONES, D., Wu, R., Tsai, B. and Harvey, J. 2011. Warm-Mix Asphalt Study: Test Track
Construction and First-Level Analysis of Phase 3b HVS and Laboratory Testing (Rubberized
Asphalt, Mix Design #2). Davis and Berkeley, CA: University of California Pavement Research
Center. (UCPRC-RR-2011-03).
8 UCPRC-SR-2013-03
4. LABORATORY TESTING: BINDER AGING
4.1 Introduction
The use of warm-mix asphalt technologies allows reduced
production temperatures at the plant and during paving and
compaction. These reduced temperatures are hypothesized to
impact the long-term oxidative aging behavior of the asphalt
binder in the mix. This study attempted to quantify these impacts
through characterization of field-aged unmodified and rubber-
modified binders extracted and recovered from cores sampled
from 13 test sections representing seven different WMA technologies and associated hot-mix controls.
4.2 Methodology
A dynamic shear rheometer (DSR) was used to evaluate the binder rheological properties at high
temperatures with respect to expected rutting performance. The cup-and-bob DSR testing procedure was
assessed as an alternative approach for testing rubberized binders. A bending beam rheometer (BBR) was
used to characterize low-temperature properties.
4.3 Findings
The following observations were made based on analysis of the results:
• Test results did not appear to be influenced by the warm-mix technology chemistry. However, the mix that incorporated an organic wax additive consistently showed better rutting resistance across all the tests, and this was attributed to the residual crystallization wax structure in the binder.
• All the test results appeared to be influenced by production and placement temperatures, indicating that some mixes produced at very low temperatures could be more susceptible to early rutting on pavements that experience high ambient temperatures and high traffic loading.
• Air-void content appeared to have very little effect on the rheological properties of the extracted binder over the aging period assessed, which was not expected.
• Zero shear viscosity (ZSV) was found to be a good indicator of the rheological behavior of asphalt binders with respect to rutting performance, as observed from accelerated load testing. ZSV was also found to be more suitable for describing the rutting performance of rubberized binders than the current Superpave G*/sinδ criterion.
• Viscosity-shear susceptibility was found to be a suitable parameter for understanding the shear sensitivity of rubberized binders. Viscosity-shear susceptibility increased during long-term oxidative aging due to the increased association of polar carbonyl compounds in the binder.
Dynamic Shear Rheometer
UCPRC-SR-2013-03 9
• The non-recoverable creep compliance and percent recovery parameters obtained from the multiple stress creep recovery test are useful parameters for understanding expected field rutting performance.
• Bending beam rheometer results indicated that the WMA technologies tested did not result in a grade change with respect to thermal cracking properties at low temperatures, with all binders meeting the Superpave criteria at all ages tested. Performance trends for individual binders were consistent with rutting test results.
• The warm-mix additives and associated lower production and placement temperatures generally had limited effect on aging kinetics with respect to long-term field aging, with the exception of the organic wax.
• Laboratory binder aging, specifically the rolling thin film oven test, did not always correspond to field aging.
4.4 Recommendations
A National Cooperative Highway Research Program (NCHRP) is currently being undertaken to assess
factors that influence binder aging. The findings of that study should be reviewed and the recommended
changes implemented if appropriate. Since the NCHRP study is not investigating rubberized binders, the
applicability of these recommendations to rubberized binder aging should be investigated for a range of
binder sources and field aging conditions in California.
4.5 Reports
The following report was prepared for this phase of the study:
1. FARSHIDI, F., Jones, D. and Harvey, J.T. 2013. Warm-Mix Asphalt Study: Evaluation of
Rubberized Hot- and Warm-Mix Asphalt with Respect to Binder Aging. Davis and
Berkeley, CA: University of California Pavement Research Center. (UCPRC-RR-2013-02).
10 UCPRC-SR-2013-03
5. LABORATORY TESTING: EMISSIONS
5.1 Introduction
The use of warm mix asphalt technologies allows reduced
production temperatures at the plant and during paving and
compaction. It is believed that their use also reduces emissions
from the asphalt. The purpose of this part of the study was to
develop and assess equipment for accurately measuring surface
emissions during hot- or warm-mix asphalt paving operations
and to quantify any potential environmental benefits during
paving operations with respect to the reduction of volatile and semi-volatile organic compounds and
polycyclic aromatic hydrocarbons. Asphalt plant stack emissions were not assessed as part of this study.
5.2 Methodology
This study developed and assessed equipment for accurately measuring surface emissions during hot- and
warm-mix asphalt paving operations. A transportable flux chamber was fabricated to obtain direct
measurements of reactive organic gas emissions and to estimate the fluxes of volatile (VOC) and semi-
volatile organic compounds (SVOC) for different asphalt mixes and production temperatures using gas
chromatography mass spectrometry. A study to validate the appropriateness of the method was carried out
during placement and compaction of the RHMA-G and RWMA-G test sections (three hot-mix and seven
warm-mix, all produced at different temperatures) discussed in Chapter 2. The preliminary results
indicated that the method developed was appropriate for accurately quantifying and characterizing VOC
and SVOC emissions during asphalt paving. The study was therefore extended to assess other gaseous and
particulate polycyclic aromatic hydrocarbon (PAH) emissions from four additional asphalt mixes.
Collection of PAHs through a fine particulate filter followed by a sorbent-backed filter with further gas
chromatographic/mass spectrometric analysis was investigated. The results were used to quantify the
potential benefits of using warm-mix asphalt technologies in reducing reactive organic gas emissions.
5.3 Findings
Based on the results of the study, the following general observations with regard to emissions during
asphalt paving are made:
• The developed methodology for characterizing emissions can be used to identify and quantify VOCs, SVOCs, and PAHs in asphalt fumes during production and paving activities.
Emissions Testing
UCPRC-SR-2013-03 11
• In terms of total measured volatile organic compounds, there is a significant difference (a factor of two on average) between emissions concentrations measured from loose mix (e.g., in a truck, windrow, or when tipped into the paver hopper) and those measured from the road surface immediately after compaction.
• The kinetics of emissions over time indicated that the majority of reactive organic gases are volatilized in the first hour after construction.
• Gaseous phase PAH compounds in asphalt fumes are mainly low molecular weight compounds and are present at trace levels. The concentrations varied depending on the temperature of the mix at the time of sampling.
• Particulate phase PAHs were found to be below the detection limit of this study (0.1 ng/μL) for all the mixes (hot and warm) assessed. The results confirmed that the temperature ranges at which the asphalt mixes were produced in this study (123°C to 166°C) were not high enough to initiate significant PAH formation.
The following observations were made with respect to the effect of warm-mix asphalt technologies on
emissions during paving:
• Alkane emissions consisted of n-hydrocarbons ranging from C8 to C18. Depending on the type of mix and its temperature at the time of sampling, the total alkane emissions from the warm mixes were significantly lower than those measured from the hot mixes (e.g., 117 µg/m3 from one of the warm-mixes compared to 2,516 µg/m3 from the hot-mix control).
• In some instances, specific warm mixes had higher alkane concentrations than the hot-mix controls. Although these higher concentrations are not a health or safety concern, any generalization with regard to emissions reduction through the use of warm-mix asphalt is inappropriate and should be restricted to comparisons of specific warm-mix technologies against a hot-mix control.
• PAH concentrations correlated with initial mix production temperature, with those warm-mixes produced at the lowest temperatures showing the lowest PAH concentrations.
5.4 Recommendations
The use of warm-mix asphalt should be considered on any project where emissions are a potential issue
(e.g., in urban areas). The reduction (or even elimination) of smoke, haze, and odors, common on
rubberized asphalt projects, are significant when warm-mix technologies are used in conjunction with
lower production and placement temperatures.
5.5 Reports
The following report was prepared for this phase of the study:
1. FARSHIDI, F., Jones, D. and Harvey, J.T. 2013. Warm-Mix Asphalt Study: Evaluation of
Rubberized Hot- and Warm-Mix Asphalt with Respect to Emissions. Davis and
Berkeley, CA: University of California Pavement Research Center. (UCPRC-RR-2013-03).
12 UCPRC-SR-2013-03
6. LONG-TERM FIELD PERFORMANCE
6.1 Introduction
A number of warm-mix asphalt test sections were constructed in
California between 2007 and 2010 to assess long-term
performance under selected traffic and climate conditions. A
range of pavement designs were assessed, but the six projects
evaluated in this study focused on open-graded friction courses
with polymer-modified (PG 58-34) and rubber-modified
(PG 64-16) binders (three projects each). The main purpose of these experiments was to monitor
performance under actual traffic and environmental conditions and to quantify any benefits associated
with using warm-mix asphalt under specific situations such as with long hauls, in cool and/or damp
conditions, under trafficking by large agricultural equipment, etc. Four of the test sections, which were
located near Morro Bay, Point Arena, Orland, and Mendocino, had hot-mix controls. Two additional
warm-mix asphalt projects, located near Marysville and Auburn, did not include control sections. The
warm-mix technologies assessed in these projects included Advera, Evotherm, Gencor, Rediset, and
Sasobit.
6.2 Methodology
Rubberized warm-mix asphalt (Evotherm) open-graded friction course test sections near Orland (heavy
traffic), Marysville (heavy agricultural equipment turning on road), and Auburn (OGFC overlay on
cracked pavement) were monitored biannually for up to four years. Monitoring included a visual
assessment from the shoulder and a photographic record.
6.3 Findings
All of the sections performed well. On the projects that included hot-mix control sections, the warm-mix
asphalt sections showed equal performance to the controls. On one project (Interstate-5 near Orland), the
warm-mix section showed some early minor rutting in the first six months, which was not observed on the
Control. However, after 12 months of trafficking rut depths on both sections were the same. This early
rutting on the warm-mix section was attributed to less oxidation of the binder due to the lower production
and placement temperatures. Once the rate of oxidation had stabilized (after ± 12 months), rutting
performance appeared to be the same, and to progress at the same rate, on both sections. This observation
was consistent with observations on earlier accelerated loading experiments and is not considered to be a
WMA field experiment
UCPRC-SR-2013-03 13
concern given that rut depths were the same on the control and warm mix sections at the end of the
testing/evaluation periods.
Based on the observations in this study, the use of warm-mix technologies in open-graded friction course
mixes with polymer- and rubber-modified binders appears to be beneficial, especially on projects that
require long hauls and/or placement in cold temperatures. The use of warm-mix technologies resulted in
improved workability of the mix and better compaction, which should improve durability and prevent
early raveling.
6.4 Reports
The following report was prepared for this phase of the study:
1. JONES, D. 2012. Warm-Mix Asphalt Study: Field Test Performance Evaluation. Davis and
Berkeley, CA: University of California Pavement Research Center. (UCPRC-TM-2013-08).
14 UCPRC-SR-2013-03
7. CONCLUSIONS AND RECOMMENDATIONS
7.1 Conclusions
The testing completed in this phase of the warm-mix asphalt
study has provided no results to suggest that warm-mix
technologies should not be used in rubberized mixes in
California, provided that standard specified mix design,
construction, and performance limits for hot-mix asphalt are met.
The use of warm-mix asphalt technologies in rubberized asphalt mixes has clear benefits when compared
to hot mixes. These include significant reductions in, or even elimination of, smoke and odors, lower
emissions, improved workability, better working conditions, and better performance on projects with long
hauls or where mixes are placed under cool conditions. The slightly higher costs of using warm-mix
technologies are outweighed by these benefits.
7.2 Recommendations
Based on the findings of this study, the use of warm-mix asphalt technologies in rubberized asphalt mixes
is encouraged, especially on projects in urban areas and those projects with long hauls and/or where mixes
are placed under cool conditions. Given that warm-mix asphalt may be produced at significantly lower
temperatures than hot-mix asphalt (with associated lower aggregate heating temperatures), it is
recommended that moisture sensitivity, especially with use of water-based warm-mix asphalt
technologies, is closely monitored in mix-design and quality control/quality assurance testing. Care
should also be taken on selecting production temperatures for mixes that will be placed on roads with
heavy truck traffic in hot climates, as the lower initial oxidation of the binder associated with low
production temperatures may lead to early rutting.
WMA field experiment
UCPRC-SR-2013-03 15
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16 UCPRC-SR-2013-03
REFERENCES
1. JONES, D., Wu, R., Tsai, B., Lu, Q. and Harvey, J. 2008. Warm-Mix Asphalt Study: Test Track
Construction and First-level Analysis of Phase 1 HVS and Laboratory Testing. Davis and
Berkeley, CA: University of California Pavement Research Center. (UCPRC-RR-2008-11).
2. JONES, D., Wu, R., Tsai, B., Lu, Q. and Harvey, J. 2008. Warm-Mix Asphalt Study: First-Level
Analysis of Phase 2 HVS and Laboratory Testing, and Phase 1 and Phase 2 Forensic
Assessments. Davis and Berkeley, CA: University of California Pavement Research Center.
(UCPRC-RR-2009-02).
3. JONES, D. and Tsai, B. 2012. Warm-Mix Asphalt Study: First-Level Analysis of Phase 2b
Laboratory Testing on Laboratory Prepared Specimens. Davis and Berkeley, CA: University
of California Pavement Research Center. (UCPRC-RR-2012-07).
4. JONES, D., Wu, R., Tsai, B. and Harvey, J. 2011. Warm-Mix Asphalt Study: Test Track
Construction and First-Level Analysis of Phase 3a HVS and Laboratory Testing (Rubberized
Asphalt, Mix Design #1). Davis and Berkeley, CA: University of California Pavement Research
Center. (UCPRC-RR-2011-02).
5. JONES, D., Wu, R., Tsai, B. and Harvey, J. 2011. Warm-Mix Asphalt Study: Test Track
Construction and First-Level Analysis of Phase 3b HVS and Laboratory Testing (Rubberized
Asphalt, Mix Design #2). Davis and Berkeley, CA: University of California Pavement Research
Center. (UCPRC-RR-2011-03).
6. FARSHIDI, F., Jones, D. and Harvey, J.T. 2013. Warm-Mix Asphalt Study: Evaluation of
Rubberized Hot- and Warm-Mix Asphalt with Respect to Binder Aging. Davis and Berkeley,
CA: University of California Pavement Research Center. (UCPRC-RR-2013-02).
7. FARSHIDI, F., Jones, D. and Harvey, J.T. 2013. Warm-Mix Asphalt Study: Evaluation of
Rubberized Hot- and Warm-Mix Asphalt with Respect to Emissions. Davis and Berkeley, CA:
University of California Pavement Research Center. (UCPRC-RR-2013-03).
8. JONES, D. 2012. Warm-Mix Asphalt Study: Field Test Performance Evaluation. Davis and
Berkeley, CA: University of California Pavement Research Center. (UCPRC-TM-2013-08).
UCPRC-SR-2013-03 17